(1) Field of the Invention
The present invention relates to cDNA encoding a chitin binding protein (lectin) of rhizomes of Urtica dioica (nettle lectin). The chitin binding protein (lectin) is provided in a vector for transforming plants to impart insecticidal activity to cells of the plant, particularly in the leaves of the plant.
(2) Prior Art
Chitin-binding proteins have been found in a wide range of species, including both monocots and dicots, even though plants contain no chitin. These proteins are related by the presence of a conserved 43 amino acid cysteine and glycine rich domain. In some of these proteins the chitin-binding domain has been duplicated and appears in tandem repeats. In others, this domain has been fused to an unrelated domain. In vitro experiments using many different chitin-binding proteins suggest they may be involved in plant defense against insects or fungal pathogens.
Chitin, a polymer of .beta.-1,3-N-acetyl-glucosamine, is found in the cell wall of many fungi, the exoskeleton and digestive tract of some insects and in some nematodes. It is curious then that plants, which contain no chitin, express a family of chitin-binding proteins with a conserved chitin-binding domain. These plants range from wheat to rubber trees and stinging nettle. Chitin-binding proteins are secretory proteins which may be involved in plant defense (Chrispeels, M. J. and Raikhel, N. V., Plant Cell 3:1-9 (1991)). Several genes and proteins from this family have been isolated and characterized. Some of them, for example the Gramineae lectins, have been shown to have insecticidal activity by in vitro experiments (Murdock, L. L., et al., Phytochemistry 29:85-89 (1990); Czapla, T. H. and Lang, B. A., J. Econ. Entomol. 83:2480-2485 (1991)). Others, such as the basic chitinases and hevein, possess antifungal activity in in vitro experiments (Schlumbaum, A., et al., Nature, 324:365-367 (1968); Van Parijs, J., et al., Planta, 183, 258-264 (1991)). Recently, a chitin-binding protein isolated from the rhizomes of stinging nettle (Urtica dioica) (Urtica dioica), Urtica dioica agglutinin (UDA), has been shown to possess both antifungal and insecticidal activities (Broekaert, W. F., et al., Science, 245, 1100-1102 (1989); Huesing, J. E., et al., Phytochemistry, in press (1991)).
The rhizomes of stinging nettle serve as underground storage tissues and as a source of vegetative meristems for regeneration of shoots in the spring. For both these functions rhizomes would require mechanisms for protection against soil pathogens. UDA has been found to accumulate to high levels (1 gm/kg) in the rhizomes (Peumans, W. J., et al., FEBS Letters 177:99-103 (1983)). This small protein, 8.5 kDa, is rich in glycine and cysteine residues and has been shown to have homology to other chitin-binding proteins (Chapot, M-P, et al., FEBS Letters 195:231-234 (1986)). Several isoforms, isolectins, of UDA have been isolated (Van Damme, E. J. M., and Peumans, W. J., Plant Physiol. 86:598-601 (1988)).